<template>
  <h3>笑脸跟随鼠标</h3>
</template>

<script>
export default {
  name: "index",
  methods:{
    show(){
      (function emojiCursor() {

        var possibleEmoji = ["😀", "😂", "😆", "😊"];
        var width = window.innerWidth;
        var height = window.innerHeight;
        var cursor = {x: width/2, y: width/2};
        var particles = [];

        function init() {
          bindEvents();
          loop();
        }

        // Bind events that are needed
        function bindEvents() {
          document.addEventListener('mousemove', onMouseMove);
          document.addEventListener('touchmove', onTouchMove);
          document.addEventListener('touchstart', onTouchMove);

          window.addEventListener('resize', onWindowResize);
        }

        function onWindowResize(e) {
          width = window.innerWidth;
          height = window.innerHeight;
        }

        function onTouchMove(e) {
          if( e.touches.length > 0 ) {
            for( var i = 0; i < e.touches.length; i++ ) {
              addParticle( e.touches[i].clientX, e.touches[i].clientY, possibleEmoji[Math.floor(Math.random()*possibleEmoji.length)]);
            }
          }
        }

        function onMouseMove(e) {
          cursor.x = e.clientX;
          cursor.y = e.clientY;

          addParticle( cursor.x, cursor.y, possibleEmoji[Math.floor(Math.random()*possibleEmoji.length)]);
        }

        function addParticle(x, y, character) {
          var particle = new Particle();
          particle.init(x, y, character);
          particles.push(particle);
        }

        function updateParticles() {

          // Updated
          for( var i = 0; i < particles.length; i++ ) {
            particles[i].update();
          }

          // Remove dead particles
          for( var i = particles.length -1; i >= 0; i-- ) {
            if( particles[i].lifeSpan < 0 ) {
              particles[i].die();
              particles.splice(i, 1);
            }
          }

        }

        function loop() {
          requestAnimationFrame(loop);
          updateParticles();
        }

        /**
         * Particles
         */

        function Particle() {

          this.lifeSpan = 120; //ms
          this.initialStyles ={
            "position": "fixed",
            "top": "0",
            "display": "block",
            "pointerEvents": "none",
            "z-index": "10000000",
            "fontSize": "24px",
            "will-change": "transform"
          };

          // Init, and set properties
          this.init = function(x, y, character) {

            this.velocity = {
              x:  (Math.random() < 0.5 ? -1 : 1) * (Math.random() / 2),
              y: 1
            };

            this.position = {x: x - 10, y: y - 20};

            this.element = document.createElement('span');
            this.element.innerHTML = character;
            applyProperties(this.element, this.initialStyles);
            this.update();

            document.body.appendChild(this.element);
          };

          this.update = function() {
            this.position.x += this.velocity.x;
            this.position.y += this.velocity.y;
            this.lifeSpan--;

            this.element.style.transform = "translate3d(" + this.position.x + "px," + this.position.y + "px,0) scale(" + (this.lifeSpan / 120) + ")";
          }

          this.die = function() {
            this.element.parentNode.removeChild(this.element);
          }
        }

        /**
         * Utils
         */

        // Applies css `properties` to an element.
        function applyProperties( target, properties ) {
          for( var key in properties ) {
            target.style[ key ] = properties[ key ];
          }
        }

        init();
      })();
    }
  },
  mounted() {
    this.show()
  }
}
</script>

<style scoped>

</style>
